Checking social security debts: step by step

Checking a contractor for social security and tax debts looks simple, but in practice it often goes wrong: the wrong number, a check made at the wrong moment, or a result that is never stored. This step-by-step plan walks through the whole check, from finding the company number to archiving the evidence.

Step 1: find the right company number

Every check starts from the contractor''s company number, ten digits in the form 0123.456.789. You will find it:

• on the contractor''s invoice, usually at the bottom next to the VAT number;
• in the Crossroads Bank for Enterprises, under the company name;
• in your own supplier file, if you added the contractor earlier.

Watch out for two pitfalls. Never work on the name alone: trade names occur more than once and an establishment unit is not the legal entity. And always check the entity shown on the invoice, even when the works were actually carried out by a sister company. The withholding obligation follows the payment, not the site.

Step 2: determine whether the works are covered

The check is only mandatory for works covered by article 30bis or 30ter: immovable works, plus three additional sectors, namely cleaning, meat and security. An overview per activity is on our sector pages and the legal background in article 30bis explained.

When in doubt, check anyway. An unnecessary check costs nothing, a missing check can cost the invoice amount.

Step 3: check the NSSO and FPS Finance

There are two separate debt positions, and therefore two results:

• NSSO: social security contributions. A debt leads to a withholding of 35% of the amount excluding VAT.
• FPS Finance: tax debts. A debt leads to a withholding of 15%.

For self-employed contractors without staff, the position with the NISSE also matters. We check that too.

You can consult both positions manually through the official public portals. That works for one or two numbers, but becomes unworkable once you have dozens of suppliers: you have to log in again for every number, note the result by hand and track the date yourself. For a single quick check, use our check withholding obligation page.

Step 4: read the result correctly

A check returns one of these outcomes per source:

• In order: no debt at the moment of the check. You pay the invoice in full.
• Withholding required: there is a debt. You withhold and transfer to the relevant authority.
• Out of scope: the entity is not covered by the scheme, for example because there are no employer obligations.
• Unknown: the number was not found or the source did not respond. Never treat this as a green light: fix the number first and repeat the check.

The key principle: the result is valid at the moment of payment. Last month''s check does not cover today''s payment.

Step 5: calculate the withholding, including the cap

If the contractor has debts with both the NSSO and FPS Finance, the sum would be 50%. The law caps the total withholding at 50% of the invoice amount excluding VAT. So calculate:

1. NSSO share: 35% of the amount excluding VAT, if there is a social security debt.
2. FPS share: 15% of the same amount, if there is a tax debt.
3. Cap the total at 50% of the amount excluding VAT.

Checkplicht performs this calculation automatically and shows the three amounts side by side.

Step 6: split the payment in your bookkeeping

When an amount must be withheld, the invoice leaves in two or three parts:

• the net amount to the contractor;
• the NSSO share to the NSSO, with the correct structured reference;
• the FPS share to FPS Finance, with its own reference.

The transfer goes through the official channels of the authority concerned. Checkplicht points you, per check, directly to the correct official payment tool, so you never use a wrong reference.

Step 7: archive the evidence

Without evidence, the check does not exist. Keep, per payment, the company number, the name, the date and time, the result per source, the calculated amount and, where applicable, the proof of transfer.

Checkplicht stores this automatically and delivers, per check, a certificate with a unique ID and QR verification, plus a bundle covering all your contractors and a monthly overview as PDF.

Step 8: schedule automatic re-checks

For ongoing cooperation, a one-off check is not enough. Pick a cadence, for example every 7, 14 or 30 days, and let the check run automatically. With Checkplicht you get an alert in the app and an email as soon as a withholding is detected for one of your contractors, so you never pay on outdated information.

See the pricing or create an account and test it free for seven days.

Frequently asked questions

How often must I check? At every payment, including advances and interim invoices.

I cannot find the company number, what now? Search the entity by name and registered office in the Crossroads Bank and compare with the invoice details. When in doubt, request the number in writing from the contractor before you pay.

What if the result stays unknown? Do not pay out on an unknown result. Fix the number or contact the contractor first, then repeat the check.

Must I also check self-employed contractors without staff? Yes. A debt position exists there too, among others with the NISSE, and therefore a possible withholding.